Nodes and methods for bypassing a network node in an internet protocol (ip) multimedia subsystem (ims) system

ABSTRACT

The invention relates to methods, IMS system, and nodes such as P-CSCF, I-CSCF and S-CSCF for bypassing a network node, such as the HSS, during a reregistration procedure. Communication links are monitored and if a probability of success of a new request to the network node is within a range, then the network node can be bypassed.

TECHNICAL FIELD

The present invention relates to Internet Protocol (IP) MultimediaSubsystem (IMS), methods and nodes for bypassing a network node.

BACKGROUND

In Internet Protocol (IP) Multimedia Subsystem (IMS), the clients haveto register to the network prior to receiving a service. The HomeSubscriber Server (HSS) node is a critical node in the network and ifthe HSS is unavailable to process signaling requests, then the IMSnetwork is unable to deliver services to the clients.

In Voice over Long Term Evolution (VoLTE) networks, there are manyqueries to the HSS during an attach/registration process. If the HSS isunavailable, this may lead to a critical situation where users in thenetwork, all trying to register for the service, generate masssignaling.

According to the 3GPP standards, if the Interrogating Call SessionControl Function (I-CSCF) is unable to complete the user registrationstatus query procedure User-Authorization Request (UAR) to the HSS, itshall respond back to the UE with a negative User-Authorization Answer(UAA) response; either 403 Forbidden or 480 Temporary Unavailable.

However if the HSS is in an overload condition or if there is a failurein the communication link between the HSS and the I-CSCF, there could bethousands, if not millions, of users out of service in the IMS network.When these users are unable to register or reregister, they retry anumber of times. The retry signaling creates extra signaling on all thenetwork nodes in the registration process including the P-CSCF andI-CSCF in addition to the HSS.

In some cases, the UEs, after a number of retries, attempt to reregisterin a secondary site. In this secondary site, communications channelstowards the HSS may be available but this can lead to yet more signalingload on the HSS.

In a VoLTE network, both the Evolved Packet Core (EPC) network and theIMS network signal towards the HSS and this leads to a combined total ofup to 16 signaling requests towards the HSS.

In a Voice over Wifi (VoWifi) network, whenever the UE changes accessnetworks between LTE and Wifi, the UE performs a reregistration process.

The previous examples show that the reregistration process is a frequentprocess and is a signaling intensive process. There is currently nograceful mechanism to handle a scenario where the HSS is unreachable andthe registration process is able to be successfully completed.

SUMMARY

It is therefore an object to provide a system, a method and nodes thatobviate or mitigate at least some of the above described disadvantage.

There is provided an Internet Protocol (IP) Multimedia Subsystem (IMS)system configured to determine, based on statistics of success rate ofpast requests to a network node, a probability of success of a newrequest to the network node and upon determination that the probabilityof success of the new request is within a probability of success range,to transmit a reregister request directly to a Serving Call SessionControl Function (S-CSCF) using an address of the S-CSCF provided in aService Route header, thereby bypassing the network node.

There is provided a method for bypassing a network node comprising thesteps of determining, based on statistics of success rate of pastrequests to the network node, a probability of success of a new requestto the network node and upon determination that the probability ofsuccess of the new request is within a probability of success range,transmitting a reregister request directly to a Serving Call SessionControl Function (S-CSCF) using an address of the S-CSCF provided in aService Route header, thereby bypassing the network node.

There is provided an Interrogating Call Session Control Function(I-CSCF) comprising a processing circuit and memory, said memorycontaining instructions executable by said processing circuit wherebythe I-CSCF is operative to determine, based on statistics of successrate of past requests to a Home Subscriber Server (HSS), a probabilityof success of a new request to the HSS and upon determination that theprobability of success of the new request is within a probability ofsuccess range, transmit a reregister request directly to a Serving CallSession Control Function (S-CSCF) using an address of the S-CSCFprovided in a Service Route header of the reregister request, therebybypassing the HSS.

There is provided a Proxy Call Session Control Function (P-CSCF)comprising a processing circuit and memory, said memory containinginstructions executable by said processing circuit whereby the P-CSCF isoperative to determine, based on statistics of past availabilities of aServing Call Session Control Function (S-CSCF), a probability of currentavailability of the S-CSCF and upon determination that the probabilityof current availability is within a probability of availability range,transmit a reregister request directly to the S-CSCF using an address ofthe S-CSCF provided in a Service Route header received from the S-CSCFduring an initial registration.

There is provided a Serving Call Session Control Function (S-CSCF)comprising a processing circuit and memory, said memory containinginstructions executable by said processing circuit whereby the S-CSCF isoperative to determine, based on statistics of success rate of pastrequests to a Home Subscriber Server (HSS), a probability of success ofa new request to the HSS and upon determination that the probability ofsuccess of the new request to the HSS is within a probability of successrange, accept a reregister request without updating the HSS and set up aflag for a later update of the HSS.

There is provided an Interrogating Call Session Control Function(I-CSCF) for bypassing a Home Subscriber Server (HSS), the I-CSCFcomprising a determination module for determining, based on statisticsof success rate of past requests to a Home Subscriber Server (HSS), aprobability of success of a new request to the HSS and a transmissionmodule for transmitting, upon determination that the probability ofsuccess of the new request is within a probability of success range, areregister request directly to a Serving Call Session Control Function(S-CSCF) using an address of the S-CSCF provided in a Service Routeheader of the reregister request, thereby bypassing the HSS.

There is provided a Proxy Call Session Control Function (P-CSCF) forbypassing a Home Subscriber Server (HSS) and an Interrogating CallSession Control Function (I-CSCF), the P-CSCF comprising a determinationmodule for determining, based on statistics of past availabilities of aServing Call Session Control Function (S-CSCF), a probability of currentavailability of the S-CSCF and a transmission module for transmitting,upon determination that the probability of current availability iswithin a probability of availability range, a reregister requestdirectly to the S-CSCF using an address of the S-CSCF provided in aService Route header received from the S-CSCF during an initialregistration, thereby bypassing the HSS and the I-CSCF.

There is provided a Serving Call Session Control Function (S-CSCF) forbypassing a Home Subscriber Server (HSS), the S-CSCF comprising adetermination module for determining, based on statistics of successrate of past requests to a Home Subscriber Server (HSS), a probabilityof success of a new request to the HSS and a reception module foraccepting, upon determination that the probability of success of the newrequest to the HSS is within a probability of success range, areregister request without updating the HSS and for setting up a flagfor a later update of the HSS.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a network in which the method, systemand nodes described herein may be implemented.

FIG. 2 is a signaling diagram illustrating the registration informationflow according to 3GPP TS 23.228 Release 12.

FIG. 3 is a signaling diagram illustrating the process registration ofFIGS. 2.

FIG. 4 is a signaling diagram illustrating a flow according to anembodiment.

FIG. 5 is a signaling diagram illustrating a flow according to anotherembodiment.

FIGS. 6 and 7 illustrate a flowchart of a method for updating a networknode according to an embodiment.

FIGS. 8 and 9 illustrate a flowchart of a method for bypassing a networknode according to an embodiment.

FIGS. 10-15 illustrate I-CSCF, P-CSCF and S-CSCF nodes according tofurther embodiments.

DETAILED DESCRIPTION

The various features of the invention will now be described withreference to the figures. These various aspects are described hereafterin greater detail in connection with exemplary embodiments and examplesto facilitate an understanding of the invention, but should not beconstrued as limited to these embodiments. Rather, these embodiments areprovided so that the disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.

Many aspects of the invention are described in terms of sequences ofactions or functions to be performed by elements of a computer system orother hardware capable of executing programmed instructions. It will berecognized that the various actions could be performed by specializedcircuits, by program instructions being executed by one or moreprocessors, or by a combination of both. Moreover, the invention canadditionally be considered to be embodied entirely within any form ofcomputer readable carrier or carrier wave containing an appropriate setof computer instructions that would cause a processor to carry out thetechniques described herein.

In some alternate implementations, the functions/acts may occur out ofthe order noted in the sequence of actions. Furthermore, in someillustrations, some blocks may be optional and may or may not beexecuted; these are generally illustrated with dashed lines.

The examples provided in the background section show that reregistrationis a frequent and signaling intensive process and that there iscurrently no graceful mechanism to handle a scenario where the HomeSubscriber Server (HSS) is unreachable and where the registrationprocess is able to be successfully completed.

Referring now to FIG. 1, a portion of a network is illustrated. Itcomprises a User Equipment (UE) 10, Access Nodes such as Long TermEvolution (LTE) Evolved Node B (eNB) 70 and Wifi access node 80. Notillustrated, another access point could be a fixed line access with IMS.These access nodes provide a first access towards the Internet Protocol(IP) Multimedia Subsystem (IMS) network 60, which provides services tothe UE and which comprises, among others, a Proxy Call Session ControlFunction (P-CSCF) 20, an Interrogating Call Session Control Function(I-CSCF) 30, as Serving Call Session Control Function (S-CSCF) 50 and aHSS 40.

FIG. 2 illustrates the registration information flow according to 3GPPTS 23.228 Release 12, which is the registration process in use at thedate of filing of this patent application. According to this flow, arequest for registration, step 200, is sent from a UE 10 to a P-CSCF 20.The request for registration is forwarded to the I-CSCF 30, step 202,which queries the HSS 40, step 204, and receives a response, step 206.The response to the query comprises the name of the S-CSCF 50 or itscapabilities, if the name is not known. The I-CSCF 30 then forwards theregistration request, step 208, to the S-CSCF 50, as identified by nameor capabilities. The registration is processed at step 210, and OKs arereturned at steps 212, 214 and 216.

According to the current 3GPP standard, the reregistration processfollows the same signaling flow as the initial registration process andthe signaling must traverse the P-CSCF 20, the I-CSCF 30, the HSS 40,and finally the S-CSCF 50. The initial registration and thereregistration procedures necessitate that the I-CSCF 30 sends a userregistration status or User Authorization Request (UAR) query, step 204,to the HSS 40 to determine which serving S-CSCF 50 is serving the user.If the HSS 40 is unable to respond to the request, the reregistrationprocess fails as the I-CSCF 30 does not have any routing information forthe serving S-CSCF 50.

FIG. 3 illustrates in more details how the S-CSCF process registration300. First, an update request is sent to the HSS 40, step 302, and thena response is received, step 304.

Now referring to FIG. 4, which is a signaling diagram according to afirst embodiment, during a successful initial registration procedure,the S-CSCF 50 informs the P-CSCF 20, via information in a Service Routeheader, of the address of the S-CSCF 50 that is serving the UE 10. TheUE 10 then sends a subsequent registration request, step 400. Forexample, the UE 10 may send a reregister request to update itsregistration after an expiry period. Alternatively, it could send areregister request when switching from an LTE 70 to a Wifi 80 accesspoint.

According to the current 3GPP standard, the Service Route is not usedfor routing during the reregistration process. As mentioned above, thereregistration process follows the same signaling flow as the initialregistration process. However, the P-CSCF 20 stores the Service Routeand can use the information for routing the subsequent reregisterrequests or call initiation requests.

Since the P-CSCF stores the Service Route associated with a particularUE 10 and S-CSCF 50 combination, the P-CSCF 20 can determine if the UE10 is performing an initial registration or a reregistration. Followingsuch determination, the P-CSCF 20 can indicate to the other nodes in theIMS network 60 that the registration request is in fact a reregistrationrequest. For example, when the P-CSCF has determined that theregistration request is a reregistration, it can append the ServiceRoute that was stored during the initial registration to the reregisterrequest before sending it to the I-CSCF 30, step 402.

According to the current version of the 3GPP standard, when the I-CSCF30 receives a register request from the P-CSCF 20, it cannotdifferentiate between an initial registration and a reregistration. Thepresence of the Service Route information in the reregister request cantherefore be used by the I-CSCF 30 to differentiate between an initialregistration and reregistration.

The Service Route information in the reregister request also provides aframework on how the I-CSCF 30 can decide whether to forward the requestto the S-CSCF 50 or to forward the request to the HSS 40 as per usualbehavior.

The I-CSCF 30, which now has the serving S-CSCF 50 routing informationincluded in the reregister request, can proceed to forward thereregister request to the serving S-CSCF 50, step 404. The Service routedoes not need to be included in the reregister request when sent fromthe I-CSCF to the S-CSCF.

According to this embodiment, the I-CSCF 30 keeps statistics on thesuccess rate of the transactions e.g. on the Diameter Cx/Dx interfacesto the HSS 40. The I-CSCF 30 makes use of these statistics to determineif statistically, the current UAR transaction for the reregistrationrequest has a high potential of being unsuccessful. If the potential foran unsuccessful outcome is high, e.g. within a predefined range such as10% to 100%, then the I-CSCF 30 forward the reregister request directlyto the S-CSCF 50. Of course ranges different than the ones providedherein could be used. Further, the ranges described herein could also berepresented with a single value, i.e. a threshold, to which thestatistical value could be compared. A person skilled in the art wouldrecognize that both are equivalents.

If the potential for a successful outcome is high, then the I-CSCF 30can send the UAR request to the HSS 40.

A case where the I-CSCF 30 determines to send the UAR to the HSS 40 butthat the transaction is not successful could indicate one of thefollowing scenarios: there was a response time out, there is a buffercongestion or the HSS indicates it is unable to process the request dueto overload conditions (e.g. User Authorization Answer (UAA) receivedwith 3004).

Once the S-CSCF 50 receives the registration request, it can thencontinue to process the registration, step 406. Then, OKs are returned,steps 408, 410 and 412.

FIG. 5, illustrates a reregistration with HSS 40 and I-CSCF 30 bypass.In this embodiment, the P-CSCF bypasses the HSS 40 as well as the I-CSCF30 based on slightly modified criteria compared to the previousembodiment.

In the embodiment illustrated at FIG. 5, the P-CSCF 20 keeps track ofthe availability status of the S-CSCF 50. We recall that the P-CSCF 20stores the S-CSCF 50 associated with each UE 10 already registered.

The P-CSCF 20 monitors the availability of the S-CSCF 50 during the lastregistration period. For example, if the registration period is 1 hour,and the S-CSCF 50 has not restarted within the last hour, then theP-CSCF 20 can assume that the serving S-CSCF 50 has not change duringthat reregistration period and can forward the reregistration request tothe same S-CSCF 50.

However if the P-CSCF 20 has detected that the S-CSCF 50 has restartedduring the last registration period, then the P-CSCF 20 can execute thelegacy behavior which is to forward the request to the I-CSCF 30.

The P-CSCF 20 can use, for example, the standard SIP OPTION mechanism tomonitor the availability of an S-CSCF 50. Or it can use information fromthe ongoing traffic signaling to know that an S-CSCF 50 is available ornot.

The P-CSCF maintains the S-CSCF 50 availability information during thelast registration period of a UE 10. Typically the registration periodis set to one common value for all UEs registered with the P-CSCF 20.Using the S-CSCF 50 availability status during the current registrationperiod, the P-CSCF 20 can use this information modify its behaviorduring the reregistration process.

When the reregister request is received, step 500, and there is nolocation information or contact information change (e.g. no change inP-Access-Network-Info (PANI) or contact IP address), the P-CSCF 20 canassume that the reregistration process is only for the UE's 10 updateafter a registration expiry timer. The registration expiry time is onlyof interest to the S-CSCF 50 (and the Application servers that aresubscribed to the users registration status or who received 3rd partyregistration updates) and not to the I-CSCF 30 and HSS 40.

If the P-CSCF 20 has determined that the S-CSCF 50 has had uninterruptedavailability status during the last registration period, then the P-CSCF20 can forward the reregister request directly to the S-CSCF 50, step502, therefore bypassing the I-CSCF 30 and the HSS 40. Forwarding therequest directly to the S-CSCF 50 reduces the network signaling.

There may be solutions where the contact IP address has not changed butthe location information (as identified by the PANI header) has changed.In some deployments, the change in location may be of interest to othernodes such as the HSS 40 for authorization validation. If that is thecase, then the P-CSCF 20 can forward the reregister request to theI-CSCF 30.

In other solutions, such as when a UE is handed over from LTE 70 to Wifi80 calling, there is no change in the IP address but a change in thePANI information. Typically, the change in PANI information is only ofinterest to the Application server. In this deployment, the I-CSCF 30bypass can be performed.

The steps executed by the S-CSCF 50, to update the HSS 40 about theuser's registration status with a Server-Assignment-Request (SAR), step504, when the HSS 40 is available, are illustrated in FIG. 3, previouslydescribed. Then, OKs are returned, steps 506 and 508.

When the S-CSCF receives the reregistration request, it may not be awarethat the HSS 40 or the I-CSCF 30 was bypassed during the process. Itshould normally treat the reregistration request as usual.

However, there may be some network scenarios that cause the HSS 40 toupdate the user's serving S-CSCF 50 to be another S-CSCF: S-CSCF2. Thishappens when, for example, the serving S-CSCF 50, S-CSCF1, is availablebut some other nodes in the network are unable to communicate with theS-CSCF1 due to link failure conditions. In such a case, the IMS S-CSCFrestoration procedures for terminating calls successfully delivers aterminating call to the user on another S-CSCF, S-CSCF2.

To summarize, the P-CSCF still has the address of S-CSCF1, the HSS hasthe address of S-CSCF2, S-CSCF1 still thinks that it is serving the UEbut it is S-CSCF2 that is actually serving the UE. This is not adesirable scenario.

The UE's P-CSCF and the UE's original S-CSCF, S-CSCF1, are not awarethat the UE serving S-CSCF has changed to S-CSCF2. The P-CSCF databasemay indicate that S-CSCF1 is the UE's serving S-CSCF but the HSSindicates that the S-CSCF2 is the UE's serving S-CSCF.

FIG. 6 illustrates a method 600 addressing this problem, and used fordeciding if the HSS should be updated.

When S-CSCF 1 receives the reregister request, step 602, it may alreadyhave the UE's profile downloaded, along with updated authenticationvectors, and may not need to send a Server-Assignment-Request (SAR) tothe HSS 40. The registration procedure in such a case should executesuccessfully. However, the network situation will be such that the HSShas S-CSCF2 as the user's server and the P-CSCF has S-CSCF1 as theuser's server. The originating calls, and the terminating calls will behandled by two different S-CSCFs and this will cause many unwantedbehaviors in the network.

In order to avoid such undesirable behaviors, the S-CSCF should check ifSAR should normally be sent to the HSS, step 604. If yes, then theS-CSCF may send the SAR to the S-CSCF, step 612. If no, the S-CSCF thenchecks it there is an indication that an HSS update is needed, step 606.If yes, then the S-CSCF may send the SAR to the S-CSCF, step 612. If no,then the S-CSCF continues the registration process without HSS update,step 610.

FIG. 7 illustrates a method 700 for further deciding if the HSS shouldbe updated. The S-CSCF should periodically send a SAR to the HSS toavoid a prolonged out of synchronization scenario such as describedabove. In order to do so, the S-CSCF may keep statistics on the successrate of the transaction towards the HSS 40. The statistics couldalternately be kept in another network node. The S-CSCF makes use ofthese statistics to determine if, statistically, the current SARtransaction should be sent to the HSS or not (even though the currentlogic indicates that a SAR request is not needed).

In order to do so, the S-CSCF maintains statistic on the health of thecommunication link between itself and the HSS. In many deployments, theS-CSCF and the I-CSCF may share the same communication link. Therefore,the statistics can be maintained for the shared communication link, ineither one of the nodes, in both nodes or in an altogether differentnetwork node.

The S-CSCF is provided with information regarding the health status ofthe link over the last registration period, e.g. a long term indicator,and the health status of the link for the current time period (i.e. lastminute), e.g. a short term indicator.

If the long term indicator is not good e.g. the link was not functioning100% of the time during the last registration period, and the short termindicator is good e.g. the link was functioning 90% to 100% of the timeduring the last minute, then the S-CSCF sends the SAR to the HSS. Theranges provided herein are only examples and could be different indifferent contexts.

If the long term indicator is not good, and the short term indicator isnot good, then the S-CSCF does not send the SAR to the HSS but indicatethat it needs to be sent the next time. Setting a flag is one ofnumerous ways of setting an indicator.

FIG. 8, illustrates a method, 800, according to an embodiment, where anInternet Protocol (IP) Multimedia Subsystem (IMS) system 60 isconfigured to determine, based on statistics of success rate of pastrequests to a network node, step 802, a probability of success of a newrequest to the network node, step 804, and upon determination that theprobability of success of the new request is within a probability ofsuccess range, to transmit, step 810, a reregister request directly to aServing Call Session Control Function (S-CSCF) 50 using an address ofthe S-CSCF provided in a Service Route header, thereby bypassing thenetwork node.

Alternatively, the system could be configured to initiate transmissionof the reregister request towards the S-CSCF.

When the network node is a Home Subscriber Server (HSS) 40, thedetermination and transmission are executed by an Interrogating CallSession Control Function (I-CSCF) 30 and the Service Route header isincluded in the reregister request.

In contrast, when the network node is the S-CSCF 50, the determinationand transmission are executed in a Proxy Call Session Control Function(P-CSCF) 20 and the Service Route header was received from the S-CSCFduring an initial registration.

Referring now to FIG. 9, the IMS system 60 receives a register requestfrom a User Equipment (UE) at a Proxy Call Session Control Function(P-CSCF), step 902. The P-CSCF determines that the register request is areregister request, step 904. The P-CSCF retrieves from a repository theaddress of the S-CSCF received during an initial registration of the UE,step 906. The P-CSCF 20 adds the Service Route header containing theaddress of the S-CSCF to the reregister request, step 908.

The repository of the P-CSCF can be a memory located inside the P-CSCFnode or an external memory accessible to the P-CSCF.

Returning to FIG. 8, the IMS system 60 is further configured todetermine, step 808, that the reregister request contains no changes inlocation or contact information compared to location and contactinformation provided in an initial registration and to transmit, step810, the reregister request directly to the S-CSCF 50 upon furtherdetermination that the reregister request contains no changes inlocation or contact information.

The location information may be comprised in a P-Access-Network-Info(PANI). In some alternatives it might be included in a Geo-Loc header.The contact information may be comprised in a contact header which cancomprise an IP address and/or a sip instance.

When the network node is a Home Subscriber Server (HSS) 40, the S-CSCF50, upon determination that the probability of success of the newrequest to the HSS is within the probability of success range, mayaccept the reregister request without updating the HSS 40 and may set upa flag for a later update of the HSS, step 812.

The IMS systems may be implemented in a cloud or virtualized environmentand may be a virtual IMS system, with its different components, nodesand servers either co-located in a single geographical area orgeographically dispersed in distant locations.

The method and system described above eliminate additional andunnecessary signaling to the HSS 40 and enable processing reregistrationrequests with minimal involvement of the HSS. This frees ups the HSS toprocess other signaling required for other use cases.

This is of particular benefits in situation where the HSS is unstable orif the links to the HSS are not available. With the existing solution,mass signaling due to retries and failovers are generated in suchinstances and the IMS networks become unreliable. When the users areunable to register, the S-CSCF 50 nodes deregister the users when theirregistration periods expire. When this happens on a large scale, theeffect is a major outage that can last as long as many hours.

The method and system described above make the IMS networks more robust.The method may be applied at all time or when the HSS is overloaded. Itcan also be applied in scenarios where there are infrequent changes tothe serving S-CSCF 50, thus providing efficient signaling on a networklevel.

FIG. 10 is a block diagram of an I-CSCF node 30 suitable forimplementing aspects of the embodiments disclosed herein. The I-CSCF 30comprises a processing circuit 1000 and memory 1002. The memory 1002contains instructions executable by the processing circuit 1000 wherebythe I-CSCF 30 is operative to determine, based on statistics of successrate of past requests to a Home Subscriber Server (HSS), a probabilityof success of a new request to the HSS and upon determination that theprobability of success of the new request is within a probability ofsuccess range, to transmit a reregister request directly to a ServingCall Session Control Function (S-CSCF) using an address of the S-CSCFprovided in a Service Route header of the reregister request, therebybypassing the HSS.

The I-CSCF 30 may further include a communications interface (notillustrated) for sending and receiving communications to and from othernetwork nodes, either directly or via the IMS network. Those skilled inthe art will appreciate that the block diagram of the I-CSCF 30necessarily omits numerous features that are not necessary for acomplete understanding of this disclosure.

The I-CSCF 30 may also include one or more storage media (notillustrated) for storing data necessary and/or suitable for implementingthe functionality described herein, as well as for storing theprogramming instructions which, when executed on the processing circuits1000, implement all or part of the functionality described herein.

FIG. 11 is a block diagram of a P-CSCF node 20 suitable for implementingaspects of the embodiments disclosed herein. The P-CSCF 20 comprises aprocessing circuit 1010 and memory 1012. The memory 1012 containsinstructions executable by the processing circuit 1010 whereby theP-CSCF 20 is operative to determine, based on statistics of pastavailabilities of a S-CSCF 50, a probability of current availability ofthe S-CSCF 50 and upon determination that the probability of currentavailability is within a probability of availability range, to transmita reregister request directly to the S-CSCF 50 using an address of theS-CSCF 50 provided in a Service Route header received from the S-CSCFduring an initial registration.

The P-CSCF 20 may further include a communications interface (notillustrated) for sending and receiving communications to and from othernetwork nodes, either directly or via the IMS network. Those skilled inthe art will appreciate that the block diagram of the P-CSCF 20necessarily omits numerous features that are not necessary for acomplete understanding of this disclosure.

The P-CSCF 20 may also include one or more storage media (notillustrated) for storing data necessary and/or suitable for implementingthe functionality described herein, as well as for storing theprogramming instructions which, when executed on the processing circuits1010, implement all or part of the functionality described herein.

FIG. 12 is a block diagram of an S-CSCF node 50 suitable forimplementing aspects of the embodiments disclosed herein. The S-CSCF 50comprises a processing circuit 1020 and memory 1022. The memory 1022contains instructions executable by the processing circuit 1020 wherebythe S-CSCF 50 is operative to determine, based on statistics of successrate of past requests to a Home Subscriber Server (HSS) 40, aprobability of success of a new request to the HSS and upondetermination that the probability of success of the new request to theHSS is within a probability of success range, to accept a reregisterrequest without updating the HSS and set up a flag for a later update ofthe HSS.

The S-CSCF 50 may further include a communications interface (notillustrated) for sending and receiving communications to and from othernetwork nodes, either directly or via the IMS network. Those skilled inthe art will appreciate that the block diagram of the S-CSCF 50necessarily omits numerous features that are not necessary for acomplete understanding of this disclosure.

The S-CSCF 50 may also include one or more storage media (notillustrated) for storing data necessary and/or suitable for implementingthe functionality described herein, as well as for storing theprogramming instructions which, when executed on the processing circuits1020, implement all or part of the functionality described herein.

FIG. 13 is a block diagram of another I-CSCF node 30 suitable forimplementing aspects of the embodiments disclosed herein. The I-CSCF 30is for bypassing a Home Subscriber Server (HSS) and comprises adetermination module 1100 for determining, based on statistics ofsuccess rate of past requests to a Home Subscriber Server (HSS), aprobability of success of a new request to the HSS and a transmissionmodule 1102 for transmitting, upon determination that the probability ofsuccess of the new request is within a probability of success range, areregister request directly to a Serving Call Session Control Function(S-CSCF) using an address of the S-CSCF provided in a Service Routeheader of the reregister request, thereby bypassing the HSS.

FIG. 14 is a block diagram of another P-CSCF node 20 suitable forimplementing aspects of the embodiments disclosed herein. The P-CSCF isfor bypassing a Home Subscriber Server (HSS) and an Interrogating CallSession Control Function (I-CSCF) and comprises a determination module1110 for determining, based on statistics of past availabilities of aServing Call Session Control Function (S-CSCF), a probability of currentavailability of the S-CSCF and a transmission module 1112 fortransmitting, upon determination that the probability of currentavailability is within a probability of availability range, a reregisterrequest directly to the S-CSCF using an address of the S-CSCF providedin a Service Route header received from the S-CSCF during an initialregistration, thereby bypassing the HSS and the I-CSCF.

FIG. 15 is a block diagram of another S-CSCF node 50 suitable forimplementing aspects of the embodiments disclosed herein. The S-CSCF isfor bypassing a Home Subscriber Server (HSS) and comprises adetermination module 1120 for determining, based on statistics ofsuccess rate of past requests to a Home Subscriber Server (HSS), aprobability of success of a new request to the HSS and a receptionmodule 1122 for accepting, upon determination that the probability ofsuccess of the new request to the HSS is within a probability of successrange, a reregister request without updating the HSS and for setting upa flag for a later update of the HSS.

Embodiments of the present disclosure may also be implemented ascomputer program products that are stored on computer-readable storagemediums, the computer program products including programminginstructions that are configured to cause the processing circuits tocarry out the steps described herein.

The invention has been described with reference to particularembodiments. However, it will be readily apparent to those skilled inthe art that it is possible to embody the invention in specific formsother than those of the embodiments described above. The describedembodiments are merely illustrative and should not be consideredrestrictive in any way. The scope of the invention is given by theappended claims, rather than the preceding description, and allvariations and equivalents that fall within the range of the claims areintended to be embraced therein.

1. An Internet Protocol (IP) Multimedia Subsystem (IMS) systemconfigured to: determine, based on statistics of success rate of pastrequests to a network node, a probability of success of a new request tothe network node; and upon determination that the probability of successof the new request is within a probability of success range, transmit areregister request directly to a Serving Call Session Control Function(S-CSCF) using an address of the S-CSCF provided in a Service Routeheader, thereby bypassing the network node.
 2. The IMS system of claim1, wherein the network node is a Home Subscriber Server (HSS).
 3. TheIMS system of claim 2 wherein the determination and transmission areexecuted by an Interrogating Call Session Control Function (I-CSCF) andwherein the Service Route header is included in the reregister request.4. The IMS system of claim 1, wherein the network node is the S-CSCF. 5.The IMS system of claim 4 wherein the determination and transmission areexecuted in a Proxy Call Session Control Function (P-CSCF) and whereinthe Service Route header was received from the S-CSCF during an initialregistration.
 6. The IMS system of claim 1 wherein a register request isreceived from a User Equipment (UE) at a Proxy Call Session ControlFunction (P-CSCF), wherein the P-CSCF determines that the registerrequest is a reregister request, wherein the P-CSCF retrieves from arepository the address of the S-CSCF received during an initialregistration of the UE and wherein the P-CSCF adds the Service Routeheader containing the address of the S-CSCF to the reregister request.7. The IMS system of claim 1, further configured to: determine that thereregister request contains no changes in location or contactinformation compared to location and contact information provided in aninitial registration; and transmit the reregister request directly tothe S-CSCF upon further determination that the reregister requestcontains no changes in location or contact information.
 8. The IMSsystem of claim 7 wherein the location information is comprised in aP-Access-Network-Info (PANI) and the contact information is comprised ina contact header.
 9. The IMS system of claim 2, wherein the S-CSCF, upondetermination that the probability of success of the new request to theHSS is within the probability of success range, accepts the reregisterrequest without updating the HSS and sets up a flag for a later updateof the HSS.
 10. The IMS system of claim 1 wherein the IMS system is avirtual IMS system.
 11. A method for bypassing a network node comprisingthe steps of: determining, based on statistics of success rate of pastrequests to the network node, a probability of success of a new requestto the network node; and upon determination that the probability ofsuccess of the new request is within a probability of success range,transmitting a reregister request directly to a Serving Call SessionControl Function (S-CSCF) using an address of the S-CSCF provided in aService Route header, thereby bypassing the network node.
 12. The methodof claim 11, wherein the network node is a Home Subscriber Server (HSS).13. The method of claim 12 wherein the determination and transmissionare executed by an Interrogating Call Session Control Function (I-CSCF)and wherein the Service Route header is included in the reregisterrequest.
 14. The method of claim 11, wherein the network node is theS-CSCF.
 15. The method of claim 14 wherein the determination andtransmission are executed in a Proxy Call Session Control Function(P-CSCF) and wherein the Service Route header was received from theS-CSCF during an initial registration.
 16. The method of claim 11,further comprising the steps, executed at a Proxy Call Session ControlFunction (P-CSCF), of: receiving a register request from a UserEquipment (UE) at the P-CSCF; determining that the register request is areregister request; retrieving from a repository the address of theS-CSCF received during an initial registration of the UE; and adding theService Route header containing the address of the S-CSCF to thereregister request.
 17. The method of claim 11, further comprising thesteps of: determining that the reregister request contains no changes inlocation or contact information compared to location and contactinformation provided in an initial registration; and transmitting thereregister request directly to the S-CSCF upon further determinationthat the reregister request contains no changes in location or contactinformation.
 18. The IMS system of claim 17 wherein the locationinformation is a P-Access-Network-Info (PANI) and the contactinformation is an IP address.
 19. The method of claim 12, wherein theS-CSCF, upon determination that the probability of success of the newrequest to the HSS is within the probability of success range, acceptsthe reregister request without updating the HSS and sets up a flag for alater update of the HSS.
 20. The method of claim 11 wherein the methodis executed in a virtual IMS system.
 21. An Interrogating Call SessionControl Function (I-CSCF) comprising a processing circuit and memory,said memory containing instructions executable by said processingcircuit whereby the I-CSCF is operative to: determine, based onstatistics of success rate of past requests to a Home Subscriber Server(HSS), a probability of success of a new request to the HSS; and upondetermination that the probability of success of the new request iswithin a probability of success range, transmit a reregister requestdirectly to a Serving Call Session Control Function (S-CSCF) using anaddress of the S-CSCF provided in a Service Route header of thereregister request, thereby bypassing the HSS.
 22. A Proxy Call SessionControl Function (P-CSCF) comprising a processing circuit and memory,said memory containing instructions executable by said processingcircuit whereby the P-CSCF is operative to: determine, based onstatistics of past availabilities of a Serving Call Session ControlFunction (S-CSCF), a probability of current availability of the S-CSCF;and upon determination that the probability of current availability iswithin a probability of availability range, transmit a reregisterrequest directly to the S-CSCF using an address of the S-CSCF providedin a Service Route header received from the S-CSCF during an initialregistration.
 23. The P-CSCF of claim 22, further operative to:determine that the reregister request contains no changes in location orcontact information compared to location and contact informationprovided in an initial registration; and transmit the reregister requestdirectly to the S-CSCF upon further determination that the reregisterrequest contains no changes in location or contact information.
 24. AServing Call Session Control Function (S-CSCF) comprising a processingcircuit and memory, said memory containing instructions executable bysaid processing circuit whereby the S-CSCF is operative to: determine,based on statistics of success rate of past requests to a HomeSubscriber Server (HSS), a probability of success of a new request tothe HSS; and upon determination that the probability of success of thenew request to the HSS is within a probability of success range, accepta reregister request without updating the HSS and set up a flag for alater update of the HSS. 25-28. (canceled)